bottle brush trees
Are the root systems of these tree invasive of underground drainage systems??
Bottle brush trees/shrubs from the genus Callistemon, I would not consider as having highly invasive root systems. But in Australia you have Melalueca species, some with a bottle brush type flower, which may be larger growing and more invasive.
Keep in mind that tree roots seek moisture, so planting in close proximity to drain tiles or an aging and possibly cracked sewer line may present more likelihood of root encroachment.